The present invention relates to a hydraulic drive assembly to support ancillary functions associated with engine driven vehicles. More particularly, this invention relates to a hydraulic drive system which provides improved efficiency by utilizing a variable displacement pump whereby the output flow can be varied to match system drive requirements. The invention is well-suited for smoothly and efficiently operating a cooling fan or compressor in an over-the-road vehicle.
A variety of conventional engines, including internal combustion engines, are available for powering vehicles. In the process of powering the vehicle, these engines develop considerable heat. therefore, one common ancillary function that must be performed on such vehicles is the cooling of the engine, typically with a fan system. Such fan systems typically include a fan which, continuously or intermittently on demand, pulls air through a radiator. Other ancillary function can also be accomplished by drawing power from the engine. For instance, a compressor can be driven to provide air conditioning, refrigeration or a brake system.
Typically, two types of drive systems exist for ancillary functions. In one type, direct belt drives are utilized. Electromagnetic or air cycle the drive off and on as required. With the belt drives, the ancillary drive is limited to abrupt full on or full off operation. This discrete and rapid actuation is generally noisy and results in high wear and maintenance on the components. In addition, belt drives are not dynamically adjustable to match actual ancillary system requirements. Consequently, systems that require maximum output at low engine speed have large components that generate inefficient excess output at increased engine speeds.
The second type of ancillary drive system incorporates a fixed displacement hydraulic pump with a bypass or "dump" valve for off/on cycling or modulation. The fixed displacement pump generates flow irrespective of the actual ancillary system requirements, which means that when the pump is sized to provide maximum output requirements at the lowest engine speed, it will generate excess flow at increased engine speeds. All excess flow is diverted inefficiently back to a reservoir. Furthermore, additional control valves are needed where modulation is required. Like the belt drive systems, the fixed displacement pump hydraulic drives fail to efficiently match output flow with ancillary system requirements.
Therefore, a primary object of the present invention is the provision of a hydraulic drive system which matches its output to the ancillary system requirements.
A further object of the present invention is the provision of a hydraulic drive system which utilizes electronic command signals from a computer or microprocessor system to match output flow with the ancillary system requirements.
A further object of the present invention is the provision of a hydraulic drive system to accommodate the utilization of an on-board engine or vehicle computer or microprocessor system to provide electronic command signals.
A further object of the present invention is the provision of an improved hydraulic drive system for an engine cooling fan.
A further object of this invention is the provision of a hydraulic drive system which allows fans or other ancillary devices to be remotely mounted.
A further object of the present invention is the provision of a hydraulic drive system comprising a closed loop hydraulic circuit that includes a variable displacement pump and a hydraulic motor for driving a fan or other ancillary device.
A further object of the present invention is the provision of a hydraulic drive system wherein oil is recirculated from an auxiliary hydraulic circuit and injected into the closed loop for make-up oil.
A further object of the present invention is the provision of a hydraulic drive system requiring a smaller hydraulic reservoir volume.
These and other objects will be apparent to those skilled in the art.